How Much Water is in the Pedernales?
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Thanks to the generous support from the Cynthia and George Mitchell Foundation over the past several years, the Meadows Center for Water and the Environment has been working to answer the question – How much water is in the Hill Country? At first blush this seems like a very straightforward question that merits a straightforward answer. However, the reality is that the largely hidden and unknown complexities of Hill Country hydrogeology make it challenging to answer.
In 2015, the Meadows Center focused its efforts on understanding the intricacies of the Pedernales watershed and underlying hydrogeology. It is important to first note that over the years, various aspects of the Pedernales River have been studied by several entities dating as far back as the 1950s. One such report, the Hill Country Alliance’s “The State of the Pedernales: Threats, Opportunities and Research Needs” report released in early 2015, provides an overview of the main characteristics of the watershed and summarizes many of these studies, their findings, and further research needs.
The gain-loss study conducted by the USGS in 1962 confirmed the 1956 study that the Pedernales River is a gaining stream, in other words, as one moves downstream from the headwaters, the flow rate increases due to springs, seeps, and inflows from the tributaries. Since the 1950’s, land use activities have changed that can affect the flow in the river and the groundwater-surface water interaction. Due to these changes and a large number of wells now pumping from the basin’s aquifers, it is important to know how land use change, groundwater pumpage, and the increase in demands affect the river flow today and long into the future. By further refining a gain-loss study with groundwater information using current hydrology we will be able to better identify threatened or critical river segments to guide management efforts to protect and enhance recharge, maintain river and tributary flows, and sustain the current high river water quality.
One of the first steps to determine how much water is in the Pedernales River was the Summer 2015 Hydro-blitz that is summarized in this interim report. Observations were made at 931 river and tributary sites to document the existence of flows in the river and tributaries during a summer dry spell to establish the groundwork for a future gain-loss study. An important outcome of the Hydro-blitz was the confirmation of the previous gain-loss studies’ findings that over 20 major tributaries play a vital role in sustaining and adding to the river flows, resulting in the realization that a future gain-loss study should extend into key tributaries to pinpoint priority water management areas and appropriate strategies. This will benefit the landowners, tourism, growing cities, agricultural practices and preserve the river ecology to ensure the Pedernales River continues to be one of the landmarks of the Texas Hill Country.